&EPA
United States
Environmental Protection
Agency
Office of Radiation Programs
Las Vegas Facility
P.O. Box 15027
Las Vegas NV89114
ORP/LV-78-4
July 1978
Radiation
Miscellaneous Data and
Information Collected
During Radiation Surveys
at the Former Monument
Uranium Mill Site
(1974-1975)
T:
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c
Technical Note
ORP/LV-78-4
MISCELLANEOUS DATA AND INFORMATION
COLLECTED DURING RADIATION SURVEYS AT THE
FORMER MONUMENT URANIUM MILL SITE (1974-1975)
Joseph M. Hans, Jr,
Daphne Prochaska
Gregory G. Eadie
July 1978
OFFICE OF RADIATION PROGRAMS-LAS VEGAS FACILITY
U.S. ENVIRONMENTAL PROTECTION AGENCY
LAS VEGAS, NEVADA 89114
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DISCLAIMER
This report has been reviewed by staff from the Office of
Radiation^Programs, Las Vegas Facility, U.S. Environmental
Protection Agency, and approved for publication. The mention of
trade names or commercial products does not constitute an endorse-
ment or recommendation for their use.
11
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PREFACE
The Office of Radiation Programs (ORP) of the U.S. Environ-
mental Protection Agency (U.S. EPA) carries out a national
program designed to evaluate population exposure to ionizing and
non-ionizing radiation, and to promote the controls necessary to
protect the public health and safety. In April 1974, staff from
the Office of Radiation Programs, Las Vegas Facility (ORP-LVF)
and from the U.S. Public Health Service-Indian Health Service
(U.S. PHS-IHS) conducted a radiation survey at the former
Monument Uranium Mill Site. The purpose of this report is to make
ancillary data, obtained during the surveys, available in pub-
lished literature in order to expand the data base related to
uranium mining and milling. Readers of this report are encouraged
to inform the authors of any omissions or errors. Comments or
requests for further information are also invited.
Donald W. Hendricks
Director, Office of
Radiation Programs, LVF
iii
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TABLE OF CONTENTS
Page
LIST OF FIGURES V
LIST OF TABLES vi
INTRODUCTION 1
SUMMARY 2
SITE DESCRIPTION 4
Location 4
Topography 4
Ownership 6
History of Operations 6
Present Condition of the Site 7
RADIATION SURVEY 8
ANCILLARY DATA AND MEASUREMENTS 10
Depth Measurements 10
Trenching 10
Bore Hole Logging 11
Estimates of the Radium-226 and Uranium Content in
the Diked Area 26
Soil Profiles 27
Environmental Gamma Ray Exposure Measurements 33
Ground-Water Sampling 33
REFERENCES 42
iv
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LIST OF FIGURES
Figure Page
1 Aerial Photograph of Former Monument
Uranium Mill Site Area 5
2 Soil Profile Locations Around the Former
Monument Uranium Mill Site 9
3 Trench Locations and Depth of Contaminants
Around the Monument Tailings Area 12
4 Bore Hole Locations and Depth Profiles in
Diked Area ^
5 Bore Hole Log 1 15
6 Bore Hole Log 2 16
7 Bore Hole Log 3 17
8 Bore Hole Log 4 18
9 Bore Hole Log 5 19
10 Bore Hole Log 6 20
11 Bore Hole Log 7 21
12 Bore Hole Log 8 22
13 Bore Hole Log 9 23
14 Bore Hole Log 10 24
15 Soil Profile A - Radionuclide Concentration
Versus Depth 2°
16 Soil Profile B - Radionuclide Concentration
Versus Depth 30
17 Soil Profile 1 - Radionuclide Concentration
Versus Depth 31
18 Soil Profile 2 - Radionuclide Concentration
Versus Depth 32
v
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LIST OF FIGURES (Continued)
Figure
19
20
Gamma Ray Exposure Rate Measurement
Locations
Location of Wells in the Vicinity of the Former
Monument Uranium Mill Site
Page
38
41
LIST OF TABLES
Table
1
2
Concentration of Radionuclides in Soil Profiles
Gamma Ray Exposure Rates Around the Former
Monument Uranium Mill Site
Total (Suspended and Dissolved) Radionuclide
Concentrations in Well Water Near the Former
Monument Uranium Mill Site
Page
35
39
40
VI
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INTRODUCTION
At the request of the Navajo Tribal Chairman and the U.S.
PHS-IHS, radiation surveys were conducted in 1974 at four inactive
uranium mill sites on the Navajo Reservation. The primary purpose
of these surveys was to provide an information base on which cost
estimates could be made for the decontamination of the mill site
areas and the interim stabilization of their tailings piles.
Data gathering for the information base addressed the location
and depth of the eroded tailings and the dispersal of uranium
ore.
The surveys indicated that extensive wind and water erosion
of the tailings had occurred around the mill sites and that ore
remains also contributed to the contamination of the environs. A
summary of the survey results, including general recommendations
for the site decontamination and interim stabilization of the
tailings piles, was prepared and forwarded to Tribal officials
(Hans, 1974). The techniques, survey equipment, and specific
survey results were reported later (Douglas and Hans, 1975).
During the course of the surveys, many measurements were
made and samples taken to support the findings and conclusions
made for each site. Since only the summaries of the surveys were
published, all of the measurements and sample results were not
reported in the literature. This report contains data and
measurements not previously reported. It will augment the data
base concerning uranium mill sites and provide additional informa-
tion to those organizations that manage and regulate the sites.
All data and measurements listed and discussed apply to the
former Monument Uranium Mill Site.
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SUMMARY
Two radiation surveys were conducted at the former Monument
Uranium Mill Site by staff from the Office of Radiation Programs-
Las Vegas Facility, U.S. Environmental Protection Agency, and the
U.S. PHS-IHS Window Rock, Arizona, Area Office. The first survey
was conducted in April 1974 to determine the spread and depth of
mill tailings and ore around the site caused by wind and water
erosion. The second survey, conducted in April 1975, was to
investigate the extent and use of mill tailings and uranium ore
for construction in dwellings around the mill site.
All of the data, measurements, and analytical results
collected during the surveys were not reported in the literature
because the survey results were reported in summary form and part
of the analytical results were not available for both survey
reports. Miscellaneous data and measurements not available or
used in the previous reports are presented and interpreted, where
possible, in this report.
Although the wind and water erosion of tailings and ore is
evident at the former Monument site, the extent is minimal when
compared to other inactive mill sites (Douglas and Hans, 1975).
The primary reason for this is that the slimes were hauled away
to other mill sites for processing. Since the slimes contain a
major portion of the radioactivity and are also very fine
particulates, they were not available for erosion. The remaining
tailings sands are coarse and tend to resist erosion.
The analysis of well water collected in the vicinity of the
mill site did not reveal any excessive radionuclide concentrations,
Well 1, located nearest to the mill site, did exhibit a signifi-
2
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cantly different radium-226 concentration than the other wells
sampled. This is probably due to the fact that the well is
artesian and taps a different ground-water source than the other
wells. According to the local residents, this well was drilled
to supply water for the operation of the mill.
Wind eroded contaminants around the tailings areas are generally
limited to the first few centimeters of topsoil. From profile
data, however, it appears that some leach losses have occurred to
the northeast of the new tailings pile.
During the April 1974 survey, it was noted that the diked
area east of the new tailings pile exhibited substantially higher
gamma radiation levels than other areas around the site. An
analysis of bore hole logs in this area indicates that the diked
area contains in excess of 3 Ci of radium-226. It is also
estimated that there may be as much as 11 short tons of uranium
in the diked area as a result of batch leach dumping. Further
exploration of the diked and the heap leach areas seems to be
warranted in order to assess the feasibility of recovering the
potential uranium values remaining on the mill site.
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SITE DESCRIPTION
LOCATION
The former Monument uranium ore upgrading mill is located on
the Navajo Indian Reservation. Specifically, the site is located
in Cane Valley, immediately to the east of Monument Valley, at
36055'45" North latitude and 109°53' West longitude in unsurveyed
Section 21, Township 41 North, Range 23 East, Gila and Salt River
Meridian, Apache County, Arizona (Figure 1). The Arizona-Utah
border is about five miles north of the site; and Mexican Hat,
Utah, is approximately 18 miles to the northwest.
TOPOGRAPHY
Cane Valley is bordered on the east by Comb Ridge, which
runs in a north-south direction. The cliffs and ridges west of
the site form the eastern boundary of Monument Valley. The
elevation of the mill site and tailings pile is approximately
4,900 feet above sea level. The total site comprises about 90
acres, and the land surrounding the site is barren and arid with
sparse vegetation.
There are two tailings areas on the site, the old tailings
area and the new tailings pile, which are approximately 500 feet
apart. The old tailings area contains the residue of the original
heap leach processed tailings and consists of approximately
165,000 tons (15 percent of the total) at an average depth of two
to three feet. Most of the original sand tailings from the old
tailings area were reprocessed and discharged into the larger,
new tailings pile. The new tailings pile contains approximately
935,000 tons (85 percent of the total) and is the result of the
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Figure 1. Aerial photograph of former Monument
Uranium Mill site area
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concentrator process. This pile covers 20 acres, is cone-shaped,
and stands 55 feet high (FBDU, 1977).
OWNERSHIP
The mill was originally constructed and operated by the
Vanadium Corporation of America, which was later merged into the
Foote Mineral Company. The span of construction and operation of
the site was from the summer of 1955 to 1968. Since the mill was
built on the Navajo Indian Reservation, full control of the site
reverted to the Navajo Nation after the mill was shut down and
dismantled.
HISTORY OF OPERATIONS
The upgrader and concentrator units were built to treat low-
grade ore from the nearby Monument No. 2 mine, which had formerly
shipped high-grade ore directly to Colorado for processing.
Monument No. 2 mine was discovered in 1943 and produced approxi-
mately 0.75 million tons of ore. In addition, over one million
tons of low-grade ore were mined for processing in the upgrader,
concentrator, or by heap leaching.
The upgrader, a sand-slime operation unit, was the first
plant at the site and operated from the summer of 1955 through
July 1964. In October 1964, a batch-leaching and concentrator
facility was installed at the same site and treated 1.1 million
tons of the sand tailings from the previous operation. By
November 1967, the final operation, heap-leaching 100,000 tons of
low-grade ore, was completed.
In May 1968, a U.S. PHS environmental survey was conducted
at the Monument site and results indicated that existing radiation
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levels did not exceed former Atomic Energy Commission recommended
exposure limits. However, due to diverse weather conditions that
may affect the tailings, it was recommended that they be stabilized
against wind erosion, or that periodic monitoring be carried out
to insure that significant wind erosion would not occur (Snelling,
1969) .
A "screening" survey of dwellings in the area was conducted
by the Navajo Environmental Protection Commission (NEPC) in
February 1975. It was found that uranium mill tailings and ore
had been extensively used for construction by the Cane Valley
residents. A follow-up survey of all the dwellings and structures
in the area was conducted later that year by the EPA and IHS
staffs to identify dwellings in which uranium mill tailings had
been used and to assess the resulting radiation exposures. This
subsequent survey confirmed the findings of the earlier one
(Hans and Douglas, 1975).
PRESENT CONDITION OF THE SITE
The plant has been completely dismantled, leaving only concrete
foundations, an abandoned shack on the hill at the west end of
the site, and various rubble. Some of the building materials and
equipment have been buried in the new tailings pile. There are a
few dwellings, occupied by four Navajo families, on the east and
south sides of the site. Three of these dwellings are very close
to the eastern edge of the site, with the closest located 1300
feet northeast. The Navajos use an access road which runs from
an old airstrip, past the new tailings pile, and on to their
dwellings. Livestock from a corral less than 600 feet away are
occasionally seen on the site, including sheep that are grazed in
the area. Although the tailings are reasonably resistant to wind
erosion, gamma radiation measurements made by EPA in 1974 indicate
some wind erosion is occurring. Some water erosion has been
observed, and there is evidence of it in the former ore heap
leaching area. There has been no attempt to stabilize the tailings,
7
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RADIATION SURVEY
Radiation surveys were conducted at the Monument site from
April 8 to April 13, 1974. Due to the non-availability of
electrical power in the area, no air sampling was conducted.
Radiological surveys around occupied dwellings were also not
conducted during this survey period since the principal objective
was to determine the extent of the tailings erosion by wind and
water.
Two lines were located around the mill site area (Figure 2).
One line is labeled 10 yR/hr and the other is labeled "background."
These lines are related to exposure rates from wind and water
eroded tailings only and are independent of the exposure rate
from the tailings piles. These lines indicate that if eroded
tailings and ore (exclusive of the tailings piles) were removed
from the inside of the lines, the remaining radioactive materials
outside of the line would produce an exposure rate approximately
equal to that of the line designation. Because of instrument
limitations, the background line cut-off was approximately 8
pCi/gm of radium-226, if the radium contaminants were concentrated
in the first cm depth of the soil.
Also shown on Figure 2 is the location of the new tailings
pile. Measurements made on the pile surface were generally less
than 100 yR/hr. Scattered throughout the mill area are piles and
pieces of ore which measured up to several hundred yR/hr at
contact. Because of this, the 10 yR/hr line enclosed most of the
former mill and ore storage area. The background line was not
closed to the west of the site because a large portion of the
area is exposed bedrock. In addition, the road entering the site
from the east and the wash which bisects the site in the south to
north direction were also contaminated. Some mill equipment is
buried in the south side of the wash.
8
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TO MEXICAN HAT t A2
UTAH 18 MILES
FORMER MILL AREA
NEW TAILINGS PILE
OLD TAILINGS AREA
INACTIVE URANIUM MILL SITE
MONUMENT VALLEY , ARIZONA
PROFILE
2
(Ti
1UIVIT DAT! . APfll 1974
SCALE IN FEE!
0 10O 700 300 40O
Figure 2. Soil profile locations around the former
Monument Uranium Mill site
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ANCILLARY DATA AND MEASUREMENTS
Data and measurements not previously published were depth
measurements, radionuclide concentrations as a function of depth,
background measurements, and radionuclide concentrations in local
well water. The techniques used for making the measurements as
well as the ensuing data are discussed below.
DEPTH MEASUREMENTS
The depths to which the gamma emitting radionuclides occurred
around the site environs were measured two ways. One was by
trenching and the other was by bore hole logging.
Trenching
The spread of contaminants around the mill site was
measured with a Nuclear Enterprise, NE-148-A, scintillometer with
a fabricated shield. The shield was designed such that it could
be interposed between the detector and the ground. Two measure-
ments were made with the instrument in contact with the ground:
one with the shield in place and the other without the shield in
place. The difference between the two measurements (A) was
indicative of the quantity of gamma emitting radionuclides on the
ground. Using this technique, the gamma ray "shine" component
from the nearby tailings pile was eliminated. In order to
minimize meter fluctuations, the scintillometer's time constant
was increased to 10 seconds. Some A measurements were made in
contamination-free areas around the mill site to establish a A
value for background.
At selected sites, trenches were dug at 5 cm depth
intervals. At each depth interval, including the surface, open-
10
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shield and closed-shield measurements were made. Trenching
continued until a depth was reached at which the open shield
minus the closed shield measurement was the same as the previously
determined background.
When background was reached after successive 5 cm depth
intervals, the excavation depth was recorded. Figure 3 indicates
locations around the tailings pile where depth measurements were
made. The off-pile area was gridded into 100 foot squares and the
depth (cm) was recorded in the upper left hand corner of each
square. For the most part, the eroded tailings were contained
within the first 5 cm depth in areas outside of the 10 yR/hr
line. The area on the north or lee side of the tailings pile had
tailings to a depth of 30 cm, which was due primarily to wind
erosion. The area inside and adjacent to the 10 yR/hr line on
the east side of the pile was diked. The dike was presumed to
have been built to catch process fluids from heap leaching.
Tailings and leached materials were found to depths of 100 cm in
this area. Very few depth measurements were made on the north
and west sides of the tailings pile because bedrock was exposed
in a large portion of these areas.
Wind erosion of the sand tailings at this site was not
as extensive as other Navajo Reservation sites surveyed. This is
probably because the fine portion (slimes) of mill tailings was
hauled away for further processing.
Bore Hole Logging
In order to explore the diked area previously mentioned,
a truck-mounted auger was used to drill 10 bore holes. Their
locations are shown in Figure 4. The bore holes were logged with
a gamma ray scintillation probe assembly containing a 2.54 cm by
1.27 cm diameter sodium iodide crystal. The assembly was shielded
with 1.27 cm of lead on the sides and bottom, with an 0.64 cm
wide 360° port at the crystal midline. A bore hole log for each
11
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BACKGROUND
NEW TAILINGS PILE
100 200 300ft
^ k.
SCALE
depth in centimeters
Figure 3. Trench locations and depth of contaminants
around the Monument tailings area
12
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NEW
TAILINGS PILE
Figure 4. Bore hole locations and depth profiles in
diked area
13
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auger hole is shown in Figures 5 through 14. Also shown in
Figure 4 are the depth profiles derived from trenching and from
bore hole logs.
Calibration of the logging equipment was done in a 55-
gallon oil drum filled with sand. A one-inch thick hollow
"washer" was filled with uranium mill tailings with different
concentrations of radium-226. The "washer" was placed in the
sand filled barrel to obtain a detector response to the tailings.
This provided a calibration factor ("mR/hr-relative" versus
radium-226 concentration (pCi/gm)) for the detector. After
passing the detector through the calibration "washer" in the
barrel, the "exposure rate" decreased exponentially to background
levels. This was due to the combined shielding effects of the
lead shield and sand fill. The exponential relationship was used
with the bore hole logs to determine the depths of the contaminants
(i.e., the log was followed until the "exposure rate" decrease
matched the exponential decrease established with the calibration
barrel). The estimated average radium-226 concentration in the
bore holes was made using the calibration curve for the logging
probe. Adjustments were made for the thickness of the radium-226
contamination.
The log for each hole began 10 cm above the hole
surface and is noted as minus 10 cm on the vertical axis of the
logs. The subsurface locations of radium-226 are indicated by the
dashed lines on the bore hole log figures. With the exception of
the first 20-cm depth, bore hole 1 (Figure 5) can be considered
as a background log. The average "exposure rate" for the back-
ground portion was 0.15 mR/hr-relative. Bore hole log 2 (Figure
6) indicated radium-226 to a depth of 40 cm below grade and an
average radium-226 concentration of 950 pCi/gm. Although the
surface was contaminated, most of the contamination was located
at about 20 cm below grade.
14
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-10-
0-
20-
40-
60-
E 80-
_o_
I
0.
120-
140-
160-
180-
200-
0.2
0.4
0.6
0.8 1.0
METER READING
(mR/hr-relative)
1.2 1.4
1.6
1.8
Figure 5. Bore hole log 1
15
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-10-
0-
20-
40-
60-
E 80-
cj,
t
120-H
160-
180-
200-
20
25
METER READING
(mR/hr-relative)
40
45
Figure 6. Bore hole log 2
16
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-10-
0-
20-
40-
60-
£ 80-
u
UJ 100-
120-
140-
160-
180-
200-
I
10
20 30 40 50
METER READING
(mR/hr-relative)
60
70
80
90
Figure 7. Bore hole log 3
17
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200
METER READING
(mR/hr-relative)
Figure 8. Bore hole log 4
18
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200
METER READING
(mR/hr-relative)
Figure 9. Bore hole log 5
19
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-10
OH
20-
40-
60-
E 80-
o
120-
140-
160-
180-
200-
1 I I I I \
0.2 0.4 0.6 0.8 1.0 1.2
METER READING
(mR/hr-relative)
1.4
1.6 1.8
Figure 10. Bore hole log 6
20
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-10-
0-
20-
40-
60-
E 80-
u
x
Q.
100-1
120-
140-
160-
180-
200-
5
15
30
METER READING
(mR/hr-relative)
Figure 11. Bore hole log 7
40
45
21
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-10-
0-
20-
40-
60-
E 80-
i^
z
a
120-
140-
160-
180-
200-
4 5
METER READING
(mR/hr-relative)
Figure 12. Bore hole log 8
22
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-10-
0-
20-
40-
60 H
£ 80-
i
100-
120-
140-
160-
180-
200-
40
s'o
60
METER READING
(mR/hr-relatlve)
90
Figure 13. Bore hole log 9
23
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-10-
0-
20-
40-
60-
E 80-
Q
I
a
120-
140-
160-
180-
200-
,'s
20
25
30
40
45
METER READING
(mR/hr-relative)
Figure 14. Bore hole log 10
24
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Bore hole log 3 (Figure 7) indicates two distinct peaks
below grade occurring at about 35 and 85 cm below grade. The
average radium-226 concentration was 750 pCi/gm and the depth of
the contaminants is estimated to extend to about 100 cm below
grade.
Bore hole log 4 (Figure 8) indicates surface contamina-
tion which increases and peaks at approximately 50 cm below
grade. The depth of the contaminants was 60 cm and the average
radium-226 concentration was 130 pCi/gm.
Bore hole log 5 (Figure 9) indicates surface contamina-
tion extending to a depth of 30 cm. The average radium-226
concentration is estimated to be 260 pCi/gm.
Bore hole log 6 (Figure 10) indicates surface contamina-
tion to a depth of 20 cm and an average radium-226 concentration
of 15 pCi/gm.
Bore hole log 7 (Figure 11) is indicative of sub-
surface contamination to a depth of 35 cm below grade having an
average radium-226 concentration of 280 pCi/gm.
Bore hole log 8 (Figure 12) indicates contamination to
a depth of 20 cm and a concentration of 460 pCi/gm.
Bore hole log 9 (Figure 13) indicates sub-surface
contamination, most of which lies between 20 and 90 cm below
grade. The average radium-226 concentration is relatively high
at 800 pCi/gm.
Bore hole log 10 (Figure 14) indicates surface contamina-
tion down to a depth of 35 cm below grade having an average
concentration of 240 pCi/gm.
25
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ESTIMATES OF THE RADIUM-226 AND URANIUM CONTENT IN DIKED AREA
The radioactive contents of the diked area were originally
presumed to have resulted from drainage from the new tailings
pile. Further checking, however, indicated that the materials in
the diked area may have come from the batch-leach process (Haldane,
1978). Apparently, this process was never very successful
because the batch tanks frequently became plugged due to the high
clay content of the ore and the contents of the tanks were dumped
in the diked area. Since no uranium separation occurred at the
mill, the uranium should be in radioactive equilibrium with the
radium-226 content of the diked area. A surface sample was taken
from the "hotter" area of the diked area and the radiochemical
analysis indicated a radium-226 concentration of 1300 pCi/gm.
Unfortunately, the uranium analysis for this sample was lost.
The total volume of the leach losses in the diked area is:
length - 650 feet
width - 250 feet
average depth - 1.5 feet
volume (ft3) = 2.4 x 105 ft3
The estimated average concentration of radium-226, based on
the bore hole logs is:
Average Adjusted Average
Log Number Concentration (pCi/gm) Concentration (pCi/gm)*
1 1.5 1.5
2 950 450.0
3 750 542.0
4 130 65.0
5 260 260.0
6 15 15.0
7 280 280.0
8 460 230.0
9 800 620.0
10 240 240.0
Z = 3886 Z = 2703
*The adjusted average radium concentration is the average concentra-
tion between the ground surface and the maximum depth at which
the radium was detected (i.e., below-grade radium concentrations
were averaged to the surface).
26
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Adjusted average radium-226 concentration 'v 300 pCi/gm
Total weight of leach losses:
Weight (gm) = (2. 4xl05f t3) (2. 88x10 " cm3 /ft3) (1.6gm/cm3) = I.lxl010gm
Total radium-226 content of impoundment:
Radium-226 (Ci) = I.lxl010gm x 300 pCi/gm = 3.3xl0.12pCi or 3.3 Ci
Assuming that uranium-238 is in equilibrium with the radium-
226, the weight of uranium-238 in the impoundment is:
Weight of Uranium-238
in the diked area^3.3 Ci(uranium-238)x(3xl06gm/Ci)
^9.9xl06gim,22,000 Ibs.
No bore holes were drilled in the old tailings area. Some
additional uranium may be present in this area from heap-leach
losses.
SOIL PROFILES
Four off-pile profile trenches were dug along the lOyR/hr
line in order to examine the radionuclide distribution as a
function of depth (Figure 2). The profile samples were obtained
by digging a trench and sampling from the side of the exposed
trench wall. The sampling intervals were 5 cm and all soil
collected in the interval was mixed and portioned into aliquots
for radiochemical analysis.
Samples were collected to a depth of 20 cm in profile A and
the radionuclide concentration versus depth is indicated on
Figure 15. The radium-226 concentrations dropped by a factor of
nearly 10 from the 0-5 cm depth to the 5-10 cm depth and rose
back to nearly the original surface concentration at a depth of
15-20 cm. The uranium concentrations exhibited a reduction of
27
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I Th-230
U-234
U-235
-102-
z
o
oc o»
o "
O
O
-10-1-
-10-J-
15
-10-3—
- - Th-232
25
DEPTH (cm)
15
25
Figure 15.
Soil profile A - Radionuclide concentration
versus depth
28
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approximately 76 percent between the 0-5 and 5-10 cm depths
and essentially remained constant at the 10-15 cm depth. Thorium-
230 decreased at approximately the same rate as the uranium.
Very little thorium-232 was present in the tailings as it was
relatively constant with depth. The apparent ratios of the
concentration of radium to uranium indicates that the contaminants
were heap leached sand tailings.
Figure 16 depicts the decrease of the listed radionuclides
as a function of depth at profile B location. The surface
concentrations of the uraniums, radium and thorium-230 are more
closely in equilibrium than those in profile A. This seems to
indicate that some ore or slimes were the principal contaminants.
It is possible that some seepage from the tailings pile or the
batch leach area occurred at this location.
The uranium and thorium-230 concentrations in profile 1
follow each other closely as a function of depth (Figure 17).
The radium-226 concentrations, however, increase sharply at the
15-20 cm depth and return to less than 1 pCi/gm at the 20-25 cm
depth. Thorium-232 exhibits a relatively constant concentration
between the surface and 25 cm depth. The ratio of the radium
concentration to the thorium-230 and uranium concentrations seems
to indicate that the contamination, for the most part, is dominated
by slimes.
Profile 2 was made outside of the diked area previously
discussed (Figure 18). The uranium-238 and uranium-234 concentra-
tions increase abruptly from the 0 to 25 cm depth and then
decrease. The radium-226 concentrations generally follow the
uranium concentrations as a function of depth, but are a factor
of approximately 30 lower. Thorium-230 concentrations increase
from 0 to 15 cm and then decrease very rapidly to the 35 cm
depth. Since the profile was made outside but adjacent to the
dike, it probably represents dike seepage. Since uranium is
generally more soluble than radium, it would be expected to
29
-------
Th-230
- U-235
U-234 -- 2 o; --
-102-
—10' —
Ra-226
—10°—
z
O
H
tu S
o
o
u
— 10-1-
-10-2-
15
-10-3-
_. Th-232
U-238
25
DEPTH (cm)
15
25
Figure 16.
Soil profile B - Radionuclide concentration
versus depth
30
-------
Th-230
U-234
U-235
-102-
—10' —
—10° —
z
o
z o
til 3
o
z
o
o
-10-'-
-10-2-
U)
CO
o
CO
in
ex
o
CM
in
10
20
-ID'3—
30
DEPTH (cm)
Figure 17.
Soil profile 1 - Radionuclide concentration
versus depth
31
-------
20
30
DEPTH (cm)
10
20
30
Figure 18.
Soil profile 2 - Radionuclide concentration
versus depth
32
-------
penetrate the dike more readily. It appears that the thorium-230
was either held up more readily in the diked area or that it was
more soluble than the uranium and was diluted and carried to
greater depths than those sampled.
The radionuclide concentrations and their two sigma counting
errors are listed in Table 1.
ENVIRONMENTAL GAMMA RAY EXPOSURE MEASUREMENTS
Gamma ray exposure rate measurements were made around the
vicinity of the tailings piles during surveys of dwellings in
Cane Valley, Arizona (Hans and Douglas, 1975). The measurements
were made with a Reuter-Stokes RS-111 pressurized ion chamber
(PIC) at three feet above the ground. Although the average gamma
ray exposure rate was reported (Hans and Douglas, 1975) , the
individual exposure rates were not reported. Figure 19 indicates
the locations where the gamma ray exposure rates were made.
Table 2 lists the measurement values.
The exposure rate at location B2 is probably anomalous
because it was made near the airstrip which had some scattered
ore or tailings use. Location B9 was probably somewhat elevated
because of its proximity to the tailings pile.
GROUND-WATER SAMPLING
Several drinking water wells were sampled during the surveys
of the Cane Valley residential locations (Hans and Douglas,
1975). Only the radium-226 concentrations were available at the
time of the previous report preparation. Radium-226 concentra-
tions in well water as well as other radionuclide concentrations
are listed in Table 3. The well locations are shown in Figure
20.
33
-------
The radium-226 concentration exceeded 1 pCi/1 in only one
well (well 1). Thorium concentrations were generally below 0.1
pCi/1, with the exception of well 3. The highest uranium-238
concentration observed was 6.1 pCi/1 in well 4. This is approxi-
mately 18 yg/1.
34
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TABLE 1. CONCENTRATION OF RADIONUCLIDES IN SOIL PROFILES
Profile
1
1
1
1
1
1
2
Depth
(cm)
0-5
5-10
10-15
15-20
20-25
0-5
5-10
10-15
15-20
20-25
0-5
5-10
10-15
15-20
20-25
0-5
5-10
10-15
15-20
20-25
0-5
5-10
10-15
15-20
20-25
0-5
5-10
10-15
15-20
20-25
0-5
5-10
10-15
15-20
20-25
25-30
Radionuclide
Ra-226
U-234
U-235
U-238
Th-230
Th-232
Ra-226
Concentration ± Two-Sigma
Counting Error (pCi/gm)
2.2 ±
1.1 ±
.82 ±
.29 ±
.96 ±
1.2 ±
.85 ±
.37 ±
.24 ±
.26 ±
.04 ±
.025 ±
.014 ±
LT.011 ±
.013 ±
1.4 ±
.91 ±
.39 ±
.25 ±
.21 ±
1.8 ±
1.2 ±
.47 ±
.29 ±
.29 ±
.33 ±
.33 ±
.21 ±
.30 ±
.31 ±
36. ±
1.5 ±
1.2 ±
1.6 ±
.62 ±
.86 ±
.28
.20
.17
.99
.19
.13
.11
.06
.055
.051
.02
.017
.012
—
.012
.14
.11
.061
.056
.046
.13
.10
.065
.053
.050
.056
.054
.043
.053
.051
1.1
.23
.20
.24
.15
.17
LT = Less than the minimum detectable activity
35
-------
TABLE 1. CONCENTRATION OF RADIONUCLIDES IN SOIL PROFILES
(Continued)
Profile
2
2
2
2
2
A
A
Depth
(cm)
0-5
5-10
10-15
15-20
20-25
25-30
0-5
5-10
10-15
15-20
20-25
25-30
0-5
5-10
10-15
15-20
20-25
25-30
0-5
5-10
10-15
15-20
20-25
25-30
0-5
5-10
10-15
15-20
20-25
25-30
0-5
5-10
10-15
0-5
5-10
10-15
Radionuclide
U-234
U-235
U-238
Th-230
Th-232
Ra-226
U-234
Concentration ±Two-Sigma
Counting Error (pCi/gm)
1.4 ±
23. ±
49. ±
53. ±
11. ±
4. ±
LT.065 ±
1.3 ±
1.9 ±
2.4 ±
.43 ±
.16 ±
1.2 ±
23. ±
49. ±
56. ±
11. ±
3.8 ±
1.3 ±
18. ±
1.2 ±
.61 ±
.019 ±
.092 ±
LT.045 ±
.27 ±
.062 ±
.25 ±
.0094 ±
.049 ±
6.4 ±
.91 ±
7.2 ±
1.5 ±
.33 ±
.30 ±
.32
1.5
2.8
4.3
.80
.31
_
.14
.15
.26
.067
.038
.29
1.5
2.8
4.6
.77
.30
.35
.40
.15
.072
.013
.029
_
.048
.045
.046
.0094
.022
.47
.18
.49
.15
.058
.055
LT = Less than the minimum detectable activity
36
-------
TABLE 1. CONCENTRATION OF RADIONUCLIDES IN SOIL PROFILES
(Continued)
Profile
A
A
A
A
B
B
B
B
B
B
Depth
(cm)
0-5
5-10
10-15
0-5
5-10
10-15
0-5
5-10
10-15
0-5
5-10
10-15
0-5
5-10
10-15
0-5
5-10
10-15
0-5
5-10
10-15
0-5
5-10
10-15
0-5
5-10
10-15
0-5
5-10
10-15
Radionuclide
U-235
U-238
Th-230
Th-232
Ra-226
U-234
U-235
U-238
Th-230
Th-232
Concentration ± Two-Sigma
Counting Error (pCi/gm)
.083 ±
LT.0087 ±
.013 ±
1.6 ±
.35 ±
.31 ±
4.4 ±
.57 ±
.34 ±
.25 ±
.34 ±
.35 ±
3.7 ±
.79 ±
.48 ±
2.1 ±
.38 ±
.40 ±
.086 ±
.012 ±
.016 ±
2.1 ±
.34 ±
.37 ±
2.9 ±
.051 ±
LT.014 ±
.27 ±
.044 ±
LT.015 ±
.027
.012
.16
.059
.057
.20
.074
.054
.047
.056
.055
.36
.17
.13
.18
.06
.063
.028
.011
.013
.18
.057
.06
.16
.024
.049
.002
LT = Less than the minimum detectable activity
37
-------
MONUMENT NO. 2
MINE
COMB RIDGE-
1
CANE VALLEY
NEW TAILINGS
PILE
OLD TAILINGS AREA B8
CANE VALLEY ROAO
• GAMMA RAY EXPOSURE RATE 0 1/2 I Ml
MEASUREMENT LOCATIONS , li l"1 r"h-*"i—^—^
Adapted from U.S. Energy Research and Development Admin. (1977)
Prepared by : Ford, Bacon & Davis Utah Inc.
Figure 19. Gamma ray exposure rate measurement
locations
38
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TABLE 2. GAMMA RAY EXPOSURE RATES AROUND THE FORMER
MONUMENT URANIUM MILL SITE
Gamma Exposure Rate (yR/hr)
Location Low High Average
Bl
B2
B3
B4
B5
B6
B7
B8
B9
9
17
7
8
8
8
9
9
10
11
20
9
10
10
10
11
10
12
10
18
8
9
9
9
10
9
11
.5
.5
39
-------
Well No.
TABLE 3. TOTAL (SUSPENDED AND DISSOLVED) RADIONUCLIDE
CONCENTRATIONS IN WELL WATER NEAR THE FORMER
MONUMENT URANIUM MILL SITE
Concentration (pCi/1)
Uranium-234 Radium-226 Thorium-230 Uranium-238 Thorium-232
1
2
3
4
5
LT 0.22 1.6 ± .19 LT 0.024 LT 0.15
NA 0.15±0.057 LT 0.038 NA
1.2±0.54 0.11±0.049 0.14 ±0.048 0.69±0.38
9.0±0.7 0.11±0.056 LT 0.015 6.1 ±0.49
9.9+5.2 0.25±0.082 0.033+0.024 4.3 ±2.4
LT 0.011
LT 0.030
0.13±0.046
LT 0.015
LT 0.02
Notes: LT means less than the minimum detectable activity
Two-sigma counting error noted when available
NA means no analysis
40
-------
MONUMENT NO. 2
MINE
Well 5
COMB RIDGE-
CANE VALLEY
-NEW TAILINGS
PILE
OLD TAILINGS
AREA
Well 3
Well 4
CANE VALLEY ROAO
I Well 2
1/2
I Ml
• WELL LOCATIONS
Adapted from U.S. Energy Research and Development Admin. (1977)
Prepared by: Ford, Bacon & Davis Utah Inc.
Figure 20. Location of wells in the vicinity of the
former Monument Uranium Mill site
41
-------
REFERENCES
Douglas, R., and J. Hans. "Ganuna Radiation Surveys at Inactive
Uranium Mill Sites." Technical Note ORP/LV-75-5, U.S. EPA,
Office of Radiation Programs, Las Vegas Facility, Las Vegas, NV
89114, August 1975.
Ford, Bacon, & Davis Utah, Incorporated. "Phase II-Title 1,
Engineering Assessment of Inactive Uranium Mill Tailings, Monument
Valley Site, Monument Valley, Arizona." Prepared for U.S. ERDA,
Grand Junction, CO, March 31, 1977.
Haldane, E. U.S. Department of Energy, Grand Junction, CO,
personal communication, April 1978.
Hans, Joseph M., Jr. "Recommendations for the Decontamination of
Uranium Mill Sites on the Navajo Reservation." U.S. EPA, Office
of Radiation Programs, NERC-LV, Las Vegas, NV 89114, October
1974.
Hans, Joseph M., Jr. and Richard L. Douglas. "Radiation Survey
of Dwellings in Cane Valley, Arizona and Utah, for Use of Uranium
Mill Tailings." Office of Radiation Programs, U.S. EPA, August
1975.
Snelling, Robert N. "Environmental Survey of Uranium Mill Tailings
Pile, Monument Valley, Arizona." U.S. Public Health Service,
Southwestern Radiological Health Laboratory, August 1969.
42
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
. REPORT NO.
ORP/LV-78-4
2.
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
Miscellaneous Data and Information Collected
During Radiation Surveys at the Former
Monument Uranium Mill Site (1974-1975)
5. REPORT DATE
July 1978
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Joseph M. Hans, Jr., Daphne Prochaska,
Gregory G. Eadie
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Office of Radiation Programs
U.S. Environmental Protection Agency
P.O. Box 15027
Las Vegas, NV 89114
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
Office of Radiation Programs
U.S. Environmental Protection Agency
P.O. Box 15027
Las Vegas, NV 89114
13. TYPE OF REPORT AND PERIOD COVERED
Technical Note
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
During April 1974, staff from the U.S. Environmental Protection Agency
and the U.S. Public Health Service/Indian Health Service conducted rad-
iation surveys at four inactive uranium mill sites on the Navajo Reser-
vation. The purpose of the surveys was to delineate the spread and
depth of ore and mill tailings in order that cost estimates could be
made for their removal and interim stabilization of the tailings piles.
The results of the surveys were prepared in summary form and very little
data was made available. This report presents the data and information
collected at the former Monument Uranium Mill site. The data includes
gamma radiation background measurements, bore hole logging data, ground
water analysis, gamma surveys, and radionuclide concentrations versus
depth in soil. Interpretation of the data is made where possible.
It appears, from bore hole logs, that a substantial amount of uranium
is still present at the mill site.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS C. COSATI Field/Group
Uranium Series
Gamma Radiation
Uranium Mill Tailings
Environmental Surveys
Radiation Surveys
Uranium Mill Tailings
1806
1807
1808
18. DISTRIBUTION STATEMENT
Unlimited
19. SECURITY CLASS (This Report)
NA
21. NO OF PAGES
49
20. SECURITY CLASS (This page)
22. PRICE
EPA Form 2220—1 (Rev. 4-77) PREVIOUS EDITION is OBSOLETE
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